add tests for unused_braces

src/test/ui/const-generics/unused_braces.rs

@@ -0,0 +1,13 @@
+// check-pass
+#![warn(unused_braces)]
+
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+struct A<const N: usize>;
+
+fn main() {
+    let _: A<7>; // ok
+    let _: A<{ 7 }>; //~ WARN unnecessary braces
+    let _: A<{ 3 + 5 }>; // ok
+}

src/test/ui/const-generics/unused_braces.stderr

@@ -0,0 +1,20 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/unused_braces.rs:4:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: unnecessary braces around const expression
+  --> $DIR/unused_braces.rs:11:14
+   |
+LL |     let _: A<{ 7 }>;
+   |              ^^^^^ help: remove these braces
+   |
+note: the lint level is defined here
+  --> $DIR/unused_braces.rs:2:9
+   |
+LL | #![warn(unused_braces)]
+   |         ^^^^^^^^^^^^^
+

src/test/ui/lint/unused_braces.rs

@@ -0,0 +1,31 @@
+// check-pass
+#![warn(unused_braces, unused_parens)]
+
+fn main() {
+    let _ = (7);
+    //~^WARN unnecessary parentheses
+
+    let _ = { 7 };
+    //~^ WARN unnecessary braces
+
+    if let 7 = { 7 } {
+        //~^ WARN unnecessary braces
+    }
+
+    let _: [u8; { 3 }];
+    //~^ WARN unnecessary braces
+
+    // do not emit error for multiline blocks.
+    let _ = {
+        7
+    };
+
+    // do not emit error for unsafe blocks.
+    let _ = unsafe { 7 };
+
+    // do not emit error, as the `{` would then
+    // be parsed as part of the `return`.
+    if { return } {
+
+    }
+}

src/test/ui/lint/unused_braces.stderr

@@ -0,0 +1,36 @@
+warning: unnecessary parentheses around assigned value
+  --> $DIR/unused_braces.rs:5:13
+   |
+LL |     let _ = (7);
+   |             ^^^ help: remove these parentheses
+   |
+note: the lint level is defined here
+  --> $DIR/unused_braces.rs:2:24
+   |
+LL | #![warn(unused_braces, unused_parens)]
+   |                        ^^^^^^^^^^^^^
+
+warning: unnecessary braces around assigned value
+  --> $DIR/unused_braces.rs:8:13
+   |
+LL |     let _ = { 7 };
+   |             ^^^^^ help: remove these braces
+   |
+note: the lint level is defined here
+  --> $DIR/unused_braces.rs:2:9
+   |
+LL | #![warn(unused_braces, unused_parens)]
+   |         ^^^^^^^^^^^^^
+
+warning: unnecessary braces around `let` head expression
+  --> $DIR/unused_braces.rs:11:16
+   |
+LL |     if let 7 = { 7 } {
+   |                ^^^^^ help: remove these braces
+
+warning: unnecessary braces around const expression
+  --> $DIR/unused_braces.rs:15:17
+   |
+LL |     let _: [u8; { 3 }];
+   |                 ^^^^^ help: remove these braces
+

src/test/ui/lint/unused_parens_borrow.rs

@@ -0,0 +1,22 @@
+// check-pass
+#![warn(unused_braces)]
+
+// changing `&{ expr }` to `&expr` changes the semantic of the program
+// so we should not warn this case
+
+#[repr(packed)]
+struct A {
+    a: u8,
+    b: u32,
+}
+
+fn main() {
+    let a = A {
+        a: 42,
+        b: 1729,
+    };
+
+    let _ = &{ a.b };
+    let _ = { a.b };
+    //~^ WARN unnecessary braces
+}

src/test/ui/lint/unused_parens_borrow.stderr

@@ -0,0 +1,12 @@
+warning: unnecessary braces around assigned value
+  --> $DIR/unused_parens_borrow.rs:20:13
+   |
+LL |     let _ = { a.b };
+   |             ^^^^^^^ help: remove these braces
+   |
+note: the lint level is defined here
+  --> $DIR/unused_parens_borrow.rs:2:9
+   |
+LL | #![warn(unused_braces)]
+   |         ^^^^^^^^^^^^^
+